Test tube rack



FIG. 1 is a perspective view of a test tube rack showing our new design;

FIG. 2 is one end view thereof, the opposite end view being identical;

FIG. 3 is a front view thereof, the rear view being ientical;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof. 

The ornamental design for a test tube rack, as shown and described. 